In recent years, when a metallic material is processed using a processing tool (a mold), lubricants are generally omitted in order to reduce processing costs. That is, the metallic material is generally processed by a dry processing. However, if the metallic material is processed without using the lubricants (i.e., if the metallic material is processed with the aid of rust inhibitive oils which are previously applied thereto), the metallic material cannot be suitably processed because of lack of lubricity, thereby producing cracking and galling in a formed product. Also, such lack of lubricity may increase friction between the metallic material and the processing tool. Such friction may significantly reduce service life of the forming dies.
In order to solve these problems, there is a need to develop lubricants or rust inhibitors that provide excellent lubricity during the processing of the metallic material. Up to now some special lubricants have been developed. For example, Japanese Laid-open Patent Publication Number 10-279979 teaches a rust inhibitive oil solution for use in the press forming of the metallic material. This oil solution contains a rust inhibitive agent, ultrabasic calcium sulfonate, a sulfuric extreme pressure agent and potassium borate. However, this oil solution contains a boron compound (potassium borate) that is pertinent to Pollutant Release and Transfer Register (PRTR). Therefore, such an oil solution is negative from the viewpoint of environmental preservation.
Post-treatment of the processing of the metallic material may, for example, include the steps of plating or coating the product. When the product is plated or coated as the post-treatment, the metallic material must be processed by the dry processing, because the lubricants remaining on the product may cause a negative effect (e.g., surface irregularity and inferior adhesion) on a plating film or coating film of the product. If the metallic material is processed using the lubricants, the lubricants remaining on the product must be removed or washed out from the product before the product is plated or coated. However, this step may lead to increased costs.
In recent years, from a point of view of environmental concerns and production efficiency, some quick-drying lubricants for use in metal processing have been developed. The known quick-drying lubricants may generally contain a volatile lubricant base that can be naturally evaporated at ordinary temperature and pressure. The quick-drying lubricants thus formulated may omit the washing step, because the nonvolatile lubricant residues are not substantially left on the metallic material after the metallic material is processed.
However, some of the known quick-drying lubricants do not have sufficient lubricity. The insufficient lubricity may cause cracking and galling in the formed product. In addition, the insufficient lubricity cannot sufficiently reduce the friction between the metallic material and the mold. As a result, the service life of the mold cannot be sufficiently extended. In order to increase the lubricity of the quick-drying lubricants, some of the known quick-drying lubricants contain chlorine ingredients. However, the chlorine ingredients contained in the lubricants can be easily decomposed to produce undesirable decomposition products during processing or with time. The decomposition products thus produced may rust the metallic material and the processing tool. Further, the chlorine ingredients may produce harmful or toxic substances when the lubricants are incinerated. Also, the chlorine ingredients may corrode or damage incinerators. In order to solve these problems, there is a need to develop improved or nonchlorine quick-drying (volatile) lubricants that can provide substantially the same lubricity as the nonvolatile lubricants.
Up to now some nonchlorine volatile lubricants for use in metal processing have been developed. For example, Japanese Laid-open Patent Publication Number 60-19952 teaches a nonchlorine volatile lubricative composition (lubricant) for use in metal processing, which composition includes a halogenated hydrocarbon (a lubricant base) having a boiling point of 23-125° C. and a fluorine containing oil having a boiling point of 130-250. However, the halogenated hydrocarbon and the fluorine containing oil is not friendly for the environment.
Further, the quick-drying lubricants can be naturally evaporated within hours or days at ordinary temperature and pressure. Therefore, when the metallic material is processed at ordinary temperature or higher temperatures, the metallic material and the processing tool are not sufficiently lubricated. Similarly, when the metallic material is processed at high speeds, the metallic material and the processing tool are not sufficiently lubricated, because the lubricants can be more rapidly evaporated. In addition, at higher temperatures, viscosity of the lubricants is generally reduced. Such reduction of viscosity may cause lack of lubricity of the lubricants.
In order to solve this problem, the metallic material can be processed at subzero temperatures. In subzero temperatures, the lubricants can be effectively restricted from evaporating. In addition, the lubricants may generally have increased viscosity. As a result, the metallic material and the processing tool can be sufficiently lubricated during the processing.
For example, Japanese Laid-open Patent Publication Number 5-247479 teaches a lubricative composition (lubricant) for use in metal processing at subzero temperatures, which composition includes a praffinic compound (a lubricant base). The lubricant is formulated so as to be used at temperatures of −50° C. to −150° C.